India's Times Now television claimed that Modi's alliance is likely to get 306 seats, a clear majority in parliament. One poll by Neta Newsx, however, forecast the NDA falling 30 seats short of a majority.
A total of 272 seats in parliament are required for a party to form a government.
Exit polls, though, are not completely accurate and have a mixed record in a country with an electorate of 900 million people. Official results are expected on Thursday.
Dubbing exit polls "gossip," Mamata Banerjee, chief minister of the West Bengal province and a Modi critic, said she doesn't trust surveys that are used for "manipulation."
Mammoth electionsVoting ended on Sunday in the seventh and final round of India's national elections, wrapping up a six-week long electoral process.
Modi's constituency of Varanasi, Uttar Pradesh — India's renowned Hindu holy city — was one of 59 where voting took place on the final day of polling. Voting also took place in the states of Punjab, Himachal Pradesh, West Bengal, Bihar, Jharkhand, Madhya Pradesh and Chandigarh on Sunday.
Some 900 million people were eligible to vote in what is considered the world's biggest democratic process.
Read more: India elections — Narendra Modi's fandom persists despite spotty record
Tense electionThe election was billed as a referendum on Modi's government, which has implemented some policies that proved unpopular, including the demonetization of high currency bank notes.
Opposition parties have also accused Modi's right-wing Bharatiya Janata Party (BJP) of aggravating ethnic and religious tensions in India by propagating a Hindu nationalist message.
In a message on Twitter, opposition politician Rahul Gandhi criticized the Election Commission (EC), saying the election schedule was manipulated to help Modi's party.
"The EC used to be feared and respected. Not anymore," Gandhi said, without giving any details.
Observers expect Modi's BJP to stay in power but with fewer seats than it picked up in the 2014 general election.
India's electoral commission said voter turnout was around 66%, slightly higher than 58% during the previous election.
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shs,ls/sms (AP, dpa)